This invention relates generally to gas turbine engines and more particularly to an improved compressor casing for a gas turbine engine that minimizes the deleterious effect of foreign object ingestion into the engine without compromising surge margin of the engine, thereby to enhance its utility as the power plant of an aircraft.
A typical gas turbine engine comprises a compressor, a combustor and a turbine in fluid flow relation. A variant of the typical engine includes a fan disposed forwardly of the compressor and an annular by-pass duct that surrounds the compressor.
One requirement of a jet engine in the aircraft environment is that it be capable of ingesting foreign objects without catastrophic damage. The problem of foreign object ingestion has been solved in the past by merely increasing the strength of the engine components exposed to impact damage. However, strength is generally equated with weight, which, in turn, compromises performance of the aircraft. Reconciliation of such seemingly divergent performance and safety requirements requires careful design of the aircraft""s propulsion system coupled with airframe aerodynamics.
Another factor that must be considered when addressing the problem of foreign object ingestion, is preservation of the surge margin of the fan and/or compressor stages. Radially grooved compressor casings have been used heretofore on gas turbine fan and compressor stages to enhance their surge margin. Unfortunately, such heretofore-known radially grooved casings have increased fan and compressor stage susceptibility to foreign object damage. Specifically, since the radial component of velocity imparted to foreign objects by the fan or compressor blades is greater than the axial velocity thereof, radially extending casing grooves capture and entrap the debris, potentially causing catastrophic damage to the engine. Thus, there is a need for an improved casing for the fan or compressor of a gas turbine engine that minimizes entrapment of ingested debris while still offering fan and/or compressor surge margin during normal operation.
The present invention solves the aforesaid problem by utilizing a plurality of radially inwardly and axially rearwardly opening circumferential grooves in the compressor casing. The grooves are disposed slightly downstream of a line swept by the leading edge of the fan or compressor blade tip. The inclined grooves offer reduced target and entrapment area for debris. Axially spaced, circumferential fins defining the grooves are sufficiently deformable so as to close upon initial impact by debris, thus minimizing the opportunity for debris entrapment. The casing grooves are preferably used in conjunction with backswept fan or compressor blades and provide fan or compressor surge margin in the conventional manner.